This is a post with a very short shelf life. By Wednesday afternoon it will be irrelevant.

On Wednesday morning the Supreme Court will give its decision in the Judicial Review proceedings challenging the legality of the Employment Tribunal fee system. If Unison’s challenge to the regime succeeds, it will quite simply be the most dramatic judicial intervention in government policy in the whole history of employment law.

Partly for that reason I have always felt sceptical about this challenge. There is a tendency nowadays to conflate something being unfair or wrong with it being illegal. I think you can readily persuade the courts that the employment tribunal fee is bad policy – ill-thought out, unfair and with serious unintended consequences. If you doubt that the fee system has resulted in a dramatic collapse in the number of tribunal claims being brought then you need to read this post by Richard Dunstan (who has documented the impact of fees more thoroughly than anyone I know).

But the issue for the Supreme Court is not whether ET fees are bad policy; the issue is whether they are unlawful. Will the Court really be prepared to go that far?

Well maybe.

Unison’s challenge is possible because Parliament never passed an Act requiring Employment Tribunals to charge a fee. This major change in the way in which employment law works was introduced through secondary legislation. The Fees Order of 2013 was introduced under the Tribunals Courts and Enforcement Act 2007. When a Minister introduces secondary legislation he or she must act within the scope not only of the Act under which the orders or regulations are made, but also in accordance with the legal principles laid down by the courts. Unison argues that Employment Tribunal fees restrict access to justice – and that a Minister can only introduce an order which does that if the restriction goes no further than is proportionate, given the legitimate aims lying behind the decision.

That argument is based in part on The European Convention on Human Rights, Article 6 of which guarantees the right to a fair trial – and which also encompasses access to justice. it is also based on European Law in so far as the fees apply to rights (such as holiday pay) which derive from EU law. However it struck me that Unison’s key argument before the Supreme Court was that there is a general common law principle that the Minister will not disproportionately restrict access to justice without the explicit authority of an Act of Parliament.

The Government does not seem to dispute that general principle. It is not arguing that the Fees Order was entirely a matter for the discretion of the Minister. The argument is about what ‘restricting access to justice’ actually means. Unison says that if the fee deters claims that should properly be brought before the Tribunal then that is enough. The Government argues that as long as the fees are actually affordable, the fact that people may choose to save their money and not bring a claim does not mean that they are being denied access to justice.

Listening to the arguments, I think the issue that really caught the attention of the Court was the sheer irrationality of paying a hefty ET fee to pursue a very small claim. The Tribunal system was designed for small claims. Unlawful deductions from wages, for example, may concern very small sums of money that are nevertheless vital to those who have not been paid what is owed them by their employer. But to take a Tribunal case to a full hearing on that issue, the claimant has to fork out £390.

Now the Government argues that if a claimant cannot afford to pay that fee, then there is a remission system which may allow the fee to be waived. But Unison’s point – and I think the Supreme Court was sympathetic to this – is that even if you could technically afford to pay the fee, why would you? It is irrational to spend £390 in the hope of recovering £100 in unpaid wages. All litigation is a risk – and even if you win the case there is a further risk that the employer will simply not pay. The fee system, Unison say, has denied thousands of individuals access to justice by effectively rendering the pursuit of their claims pointless.

The other main plank of Unison’s case is discrimination. It seems to be accepted that women are disproportionately affected by the higher fees applicable in ‘Type B’ claims (which include sex discrimination) and the issue should therefore be whether the system is a ‘proportionate means of achieving a legitimate aim’ – essentially the same principle of justification being put forward on the access to justice point.

The Court of Appeal held that the fee system was justified despite its disproportionate impact. Will the Supreme Court agree? Listening to the arguments I thought that the Government side was given quite a rough ride by some members of the Court – who did not seem impressed with the lack of thought that had gone into setting the level of the fees, assessing their impact or in setting the criteria that would determine whether an individual qualified for remission. If I were David Barr QC, who appeared for the Government, I would have felt pretty bruised at the end of my submissions. But we can’t take that as an indication of which way the decision will go. I can certainly see the Supreme Court being highly critical of the way in which fees were introduced and the effect that they have had, and yet still deciding that the Government acted lawfully in introducing them.

But it is just possible that the Supreme Court is ready to do something dramatic and rule that a major government policy is illegal. The Court has already shown that it is prepared to put the cat among the pigeons when it comes to developing our constitutional law – think of Article 50 – and a positive result for Unison would open a new chapter in the Court’s willingness to limit the powers of the executive. It would assert the sovereignty of Parliament as expressed in Acts of Parliament as against the power of ministers to shape the law through orders and regulations slipped through with minimal scrutiny and no opportunity for amendment. It would be a very big deal and – bearing in mind the extent to which the Brexit process is likely to rely on ministers introducing secondary legislation – it would have ramifications well beyond employment law.

You can watch the judgment being given on Supreme Court Live at 9.45 on Wednesday 26 July.